BRAINTREE — Cardinal Sean P. O’Malley said today he was “kind of blindsided” by Pope Benedict XVI’s decision to retire while in office, and jokingly dismissed the suggestion that he might be chosen as the new leader of the Roman Catholic church.

“I haven’t lost any sleep about it,’’ O’Malley told reporters during an afternoon news conference at the Boston archdiocese’s headquarters here. “And I have bought a round-trip ticket so I’m counting on coming home.’’

O’Malley said he had not anticipated Benedict’s decision to retire Feb. 28 because of declining health instead of dying in office as most of his predecessors have done during the 2,000-year history of the church. Benedict is the first pope in nearly 600 years to retire.

“I was surprised as everyone else,’’ O’Malley said.

As a cardinal, O’Malley will be one of about 100 church leaders who will gather at the Vatican in Rome, where they will meet behind doors in a conclave sometime in March and vote in secret ballots to choose Benedict’s successor.

The cardinal said the selection of a new pope should take into account the candidate’s age and stamina.

O’Malley said he first thought the reports of the pope’s resignation were mistaken or jokes.

But O’Malley, one of the 11 American cardinals who will vote in the conclave, said Benedict’s almost unprecedented decision to resign underscored that the papacy is about the church not the person who leads it.

O’Malley said the cardinals need to try and make a decision that reflects not just a personal choice but one that addresses the needs of the church as a whole. He said the next pope needs to have strong intellectual capacity, communication skills, organization skills and must have led a holy life.

O’Malley praised Benedict’s leadership, saying he “generously used his superior intellectual gifts, well established through his reputation as a renowned scholar, to share his gospel of the teachings of Jesus Christ and the teachings of the church with people from all walks of life throughout the world.”

He recalled Benedict’s trip to Washington in 2008, where he met with sexual abuse victims, as “one of the most powerful experiences of my life and priesthood.”

Theologians who know O’Malley said he was qualified to lead the church, but they said they did not expect an American to ever lead the church while the United States is the world’s superpower.

They also said O’Malley has never worked in the Vatican, and has never developed the personal and professional connections among church leaders that often play a key role in who is chosen as pontiff.

O’Malley said Benedict’s decision to resign is in contrast to Pope John Paul II, who stayed on as pontiff until his death, even as he battled Parkinson’s disease.

“He stayed on when he was very debilitated,’’ O’Malley said of Pope John Paul II.

Benedict has now dramatically changed the rules.

“I think that will obviously have an effect going forward,’’ O’Malley said.